The present invention relates to an ignitor assembly for a fossil fuel-fired furnace.
Ignitors are provided in fossil fuel-fired furnaces to start or supplement the combustion activities in the furnaces. For example, in one known type of coal-fired unit, coal to be burned in the furnace is dried and pulverized in a coal mill and delivered directly from the coal mill to the load-carrying coal nozzles in the furnace. Operation of the coal mills requires that heated air be supplied to the mills for drying and conveying the coal. This air is supplied by a forced-draft fan that forces the air through an air preheater, a device that uses the hot products of combustion in the furnace to preheat the air. This preheated primary air, the air used for drying and conveying coal, is delivered with the coal to the coal nozzles and used to support combustion. The primary air is typically not sufficient in quantity to support combustion of all the coal, so secondary air is brought directly from the air preheater to the furnace to supply the rest of the air needed for combustion. The coal thus supplied with air is caused to burn due to ignition energy from the primary air, the secondary air, the heat in the coal itself, radiation and conduction from flame in the furnace, and radiation from furnace walls.
It is to be noted that almost all of these combustion energy sources presuppose that the furnace has already been operating, and, in the large furnaces used in power generation, it presupposes that the furnace has been operating for a fairly long time. Accordingly, in order to cause and sustain combustion of the coal, it is necessary to use an auxiliary fuel for warming up the furnace walls, for providing ignition flame, and for warming up the air preheater. This is usually the function of oil- or gas-fired ignitors and warm-up guns.
In a typical installation, a relatively high-capacity oil burner is started by an ignitor, and this starts the process or warming up the furnace walls and the heat-exchange surfaces of the air preheater. Once the furnace has been brought up to temperature, the coal nozzles are ignited by oil- or gas-fired ignitors or by the warm-up guns themselves.
The use of auxiliary fuel is not necessarily over when the coal nozzles have started to supply coal. At higher boiler loadsxe2x80x94that is, when the amount of coal supplied by the nozzles is greatxe2x80x94the furnace can typically maintain stable combustion of the pulverized coal. However, when the load goes down and the coal supply is thereby decreased, the stability of the pulverized coal flame is also decreased, and it is therefore common practice to use the ignitors or warn-up guns to maintain flame in the furnace, thus avoiding the accumulation of unburned coal dust in the furnace and the associated danger of explosion.
Certain portions of an ignitor mounted in a windbox compartment of a furnace are subjected to relatively high temperatures on the order of 500 degrees Fahrenheit or higher. In some conventional ignitors, there is a risk that the ignitor wire may burn up In the event that insufficient cooling air contacts the ignitor. Another risk exists in that a loosely wrapped connection between the solid rod spark plug of the ignitor and the supply lead of the external electrical power source may result in inefficient spark transfer. Accordingly, the need exists for an improved ignitor assembly for a furnace which provides a reliable spark action and which has improved survivability in a high temperature environment.
It is one object of the present invention to provide an ignitor assembly for a fossil fuel-fired furnace which advantageously permits easier installation and removal of the ignitor assembly relative to its installed disposition in the furnace.
It is a further object of the present invention to provide an ignitor assembly for a fossil fuel-fired furnace which offers ease of installation and removal of the electrical wire or lead which connects the ignitor assembly to an external electrical source.
It is an additional object of the present invention to provide an ignitor assembly for a fossil fuel-fired furnace which, in comparison to conventional ignitor assemblies, reduces and simplifies the installation process or the removal process, respectively, of the ignitor assembly.
It is yet another object of the present invention to provide an ignitor assembly for a fossil fuel-fired furnace which offers a less complex, more robust configuration thus leading to improved reliability of the ignitor assembly in comparison to conventional ignitor assemblies.
It is a further additional object of the present invention to provide an ignitor assembly for a fossil fuel-fired furnace which has a configuration that advantageously disposes temperature sensitive elements, such as the electrical supply lead connecting elements, at a relatively greater spacing from the higher temperature environments of the furnace, as compared to conventional ignitor assemblies.
It is yet a further object of the present invention to provide an ignitor assembly for a fossil fuel-fired furnace which provides a coupling means for maintaining the electrode rod in connection with the supply lead of the external electrical source which is independent of the electrical communication interface between the electrode rod and the supply lead.
These and other objects of the present invention, which are intended to provide advantages over conventional ignitor assemblies, shall become apparent from the specification in which the preferred embodiment of the ignitor assembly of the present invention will be described and claimed.
According to one aspect of the present invention, there is provided an ignitor assembly for a fossil fuel-fired combustion furnace having an electrode rod and an elongate electrode rod housing for supporting therewithin the electrode rod. The elongate housing has an opening at one axial end for receiving therethrough an external electrical source connector which is operable to supply electrical current from an external electrical source. The ignitor assembly additionally includes means for electrically interconnecting the electrode rod connector and an external electrical source connector to one another. The electrically interconnecting means is operable to establish electrical communication between the electrode rod connector and the external electrical source connector when the electrode rod connector and the external electrical source connector are disposed at respective predetermined positions relative to one another forming a communication interface through which electrical current flows between the electrode rod connector and the external electrical source connector. The ignitor assembly further includes means remote from the communication interface for biasing the electrode rod connector and the external electrical source connector into their respective predetermined positions forming the communication interface whereby a reliable electrical current path is maintained between the external electrical source and the electrode rod.
Preferably, the remote biasing means of the ignitor assembly includes means for resiliently biasing the electrode rod connector and the external electrical source connector into their respective predetermined positions forming the communication interface. Moreover, it is preferable that the electrically interconnecting means includes a contact socket secured to the external electrical source connector and having a receiving chamber for receiving therein the electrode rod connector. Additionally, it is preferred that the means for resiliently biasing includes means for engaging the contact socket to bias the contact socket in a direction toward the electrode rod connector.